【０００１】
【本発明が属する技術分野】
本発明はリン酸と金属化合物を用いた新規な希土類磁石粉末の表面処理方法に関する。
【０００２】
【従来の技術】
希土類焼結磁石に比べて希土類ボンド磁石は耐食性が悪く、特に高温多湿雰囲気下で錆の発生や磁気特性の低下が顕著であり、表面処理方法の更なる改良が求められている。
特開２００２−１２４４０６号公報には、希土類磁石粉末の粉砕時に所定量のリン酸を添加し、次いで不活性ガス中または真空中で１００℃以上４００℃未満の条件で乾燥することにより耐候性が著しく向上し、もって高耐候性のボンド磁石の製造が可能であるとの開示がある。
しかし、本発明者らの検討によると、この公報の実施例に記載の表面処理方法は実質的に後述の比較例３に相当し、耐食性が十分ではなく、改善の余地を残しているのがわかった。
【０００３】
また、「金属の化成処理」（理工出版社刊，間宮富士雄著）の第３４頁、３．１．３リン酸鉄系皮膜の生成機構において、「リン酸鉄系皮膜法に用いる処理液として、リン酸ニ水素ナトリウムと界面活性剤を含む水溶液にして、皮膜化成と脱脂とを同時に行うもの」という記載がある。しかし、この処理液を用いて希土類磁石粉末にリン酸化合物被覆処理を行っても、後述の比較例５に示すように耐食性はあまり改善されないのがわかった。
【０００４】
【特許文献１】
特開２００２−１２４４０６号公報（第５頁左欄２０行目〜右欄１４行目，表１）
【非特許文献１】
間宮富士雄著「金属の化成処理」理工出版社刊出版、昭和４８年９月１５日、ｐ３４〜３５
【０００５】
【発明が解決しようとする課題】
したがって、本発明が解決しようとする課題は、耐食性の良好な希土類ボンド磁石を製造することができる、リン酸と金属化合物を用いた新規な希土類磁石粉末の表面処理方法を提供することである。
【０００６】
【課題を解決するための手段】
上記課題を解決した本発明の希土類磁石粉末の表面処理方法は、有機溶媒中に希土類磁石粉末を分散したスラリーを作製し、次いで前記スラリー中にリン酸を添加し、次いで前記スラリー中に金属化合物を添加し、次いで真空中または不活性ガス雰囲気中で５０〜３００℃に加熱することを特徴とする。
前記金属化合物が有機溶媒中に溶解した状態で添加されるとき希土類磁石粉末の耐食性が顕著に向上するので好ましい。
【０００７】
【発明の実施の形態】
本発明の表面処理方法を適用する希土類磁石粉末は特に限定されず、希土類ボンド磁石用の希土類磁石粉末であればいずれも対象になる。
具体例としてＲ−Ｔ−Ｂ系磁石粉末（ＲはＹを含む希土類元素の少なくとも１種でありＴはＦｅまたはＦｅ及びＣｏである。例えばＮｄ−Ｆｅ−Ｂ系磁石粉末等）、あるいはＲ’−Ｔ’−Ｎ系磁石粉末（Ｒ’はＹを含む希土類元素の少なくとも１種でありＴ’はＦｅまたはＦｅ及びＣｏである。例えばＳｍ−Ｆｅ−Ｎ系磁石粉末等）が挙げられる。
【０００８】
スラリーを構成する有機溶媒は少なくともスラリー中の希土類磁石粉末を大気から遮断し、酸化を抑制する効果を有するものでなければならない。例えばエタノール、メタノールまたはプロピルアルコール等のアルコール、ケトン、低級炭化水素または芳香族化合物が挙げられる。また例えば鉱油、合成油または植物油が挙げられる。
【０００９】
良好な耐食性を得るために、スラリー中における希土類磁石粉末及びリン酸の添加量は、有機溶媒に対して０．１５〜１．０ｇ／１００ｃｃとし、０．２〜０．５ｇ／１００ｃｃとするのが好ましい。リン酸の添加量が０．１５ｇ／１００ｃｃ未満では耐食性が向上せず、１．０ｇ／１００ｃｃ超では余剰のリン酸が無駄になる。ここで言うリン酸の添加量とは８５質量％濃度の水溶液に相当するものを基準としており、例えば他濃度のものを使うのであれば８５質量％濃度に換算したものを目安とすればよい。
【００１０】
本発明に用いる金属化合物は特に限定されないが、例えば有機溶媒（アルコール等）に可溶な金属化合物が好ましい。金属化合物のうちでも水酸化物、炭酸化物、ハロゲン化物、硝酸化物、亜硝酸化物、アルコラート、キレート化合物、アルキル化物等が有用である。また、金属化合物に含まれる金属元素としては、リン酸と反応してリン酸塩を生成し、且つそのリン酸塩が難水溶性であるものが良い。例えば、アルカリ金属であるＮａ、Ｋ等、希土類金属であるＭｇ、Ｃａ、Ｎｄ、Ｓｍ等、他の典型金属であるＢ、Ａｌ、Ｓｉ等および遷移金属であるＴｉ、Ｚｒ、Ｃｒ、Ｍｏ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ａｇ、Ｚｎ等の塩が挙げられるが、特にこれに限定されない。
良好な耐食性を得るために、スラリー中の有機溶媒に対して、金属化合物の添加量を０．００５〜０．２ｇ／１００ｃｃとし、０．０１〜０．１ｇ／１００ｃｃとするのが好ましい。金属化合物の添加量が０．００５重量部未満では耐食性の向上が困難であり、０．２重量部超では耐食性の向上効果が飽和する。
【００１１】
金属化合物の溶液を添加し、混合した後のスラリーを真空中または不活性ガス雰囲気中で５０〜３００℃に加熱して乾燥する。次いで室温まで冷却する。加熱温度が５０℃未満では耐食性が悪くなり、加熱温度が３００℃超では希土類磁石粉末の熱減磁が無視できなくなる。
【００１２】
本発明の表面処理方法により希土類磁石粉末の表面に形成されるリン酸化合物皮膜の平均厚みは５〜５０ｎｍ程度である。
【００１３】
以下、実施例により本発明を詳細に説明するが、それら実施例により本発明が限定されるものではない。
【００１４】
（実施例１）
リン酸化合物被覆処理後の加熱条件と耐食性との相関を調べるために以下の検討を行った。
［表面処理に供するスラリーの作製］ １００メッシュアンダーの２−１７型Ｓｍ２Ｆｅ１７Ｎ３粗粉をイソプロピルアルコール（以後、ＩＰＡと略す）を溶媒とする湿式ボールミルにより微粉砕して平均粒径２．５μｍ（空気透過法により測定）のＳｍ２Ｆｅ１７Ｎ３微粉２０ｇが分散したスラリー（１試料分）を合計４試料分作製した。
［表面処理用添加剤］
前記スラリーに添加する表面処理剤として以下の▲１▼、▲２▼を準備した。
▲１▼リン酸０．７５ｇを１００ｃｃのＩＰＡに溶解した溶液（リン酸は８５質量％濃度の水溶液、関東化学（株）製）
▲２▼ＩＰＡ １００ｃｃにＭｇＣｌ２ ０．２ｇを溶解した溶液
［表面処理］
ＩＰＡ６０ｃｃ中にＳｍ２Ｆｅ１７Ｎ３微粉２０ｇが分散したスラリー（１試料分）をそれぞれ合計４個のビーカーに用意した。次に各ビーカーを２０，４０，６０及び８０℃にそれぞれ加熱し、次いで各ビーカー内のスラリーをそれぞれスターラーで撹拌しながら▲１▼の溶液を４０ｃｃだけ２０分間かけて添加し、混合した（この場合のリン酸添加量は０．３ｇ／ビーカーに相当する）。▲１▼の溶液を添加するのは極力均一なリン酸化合物皮膜を形成するためである。次に各スラリー中のＳｍ２Ｆｅ１７Ｎ３微粉表面にリン酸化合物皮膜が極力均一に形成されるように各ビーカーの上澄み液を５０ｃｃ捨てた。次に▲２▼の溶液を５０ｃｃ添加後１０分間スターラーで撹拌し、次いで上澄み液を捨てた。これら一連の処理の間、各ビーカー内のスラリーはそれぞれ２０，４０，６０及び８０℃に保持された。次に窒素気流中で室温で乾燥した。次にロータリーポンプで真空排気しつつ２２０℃で１時間加熱し、次いで室温まで冷却して本発明によるリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を得た。
次に、前記リン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を８０℃、相対湿度（ＲＨ）９０％に保持した恒温恒湿槽に入れて１３時間保持し、次いで室温の大気中に戻す恒温恒湿試験を行った。
図１に示すように恒温恒湿試験前／後のリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉の室温の固有保磁力Ｈｃｊ（ＶＳＭにより測定）の変化幅は小さく、本発明の表面処理方法により良好な耐食性が付与されたのがわかる。また図１から、リン酸化合物処理温度は恒温恒湿試験前／後のＨｃｊの差が小さい４０〜８０℃が好ましく、６０〜８０℃がより好ましいのがわかる。
（比較例１）
実施例１と同様にして窒素気流中で室温で乾燥したリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を得た。この真空加熱処理を施さかった微粉に対して実施例１と同様の恒温恒湿試験を行った。図２に示すように恒温恒湿試験前／後のリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉の室温の固有保磁力Ｈｃｊ（ＶＳＭにより測定）の変化幅は図１に比べて大きく、実施例１に比べて耐食性が悪いのがわかった。
（比較例２）
▲２▼の溶液の添加効果（ＭｇＣｌ２のＩＰＡ希釈効果）を確認するために以下の検討を行った。
実施例１と同様にしてスラリー中のＳｍ２Ｆｅ１７Ｎ３微粉表面にリン酸化合物皮膜が極力均一に被覆されるようにビーカーの上澄み液を５０ｃｃ捨てる処理まで行った。次に▲２▼の溶液に替えてＭｇＣｌ２０．２ｇを直接スラリーに添加後１０分間スターラーで撹拌した。これら一連の処理の間、ビーカー内のスラリーを６０℃に保持した。以降は実施例１と同様にして比較例のリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を得た。この微分の恒温恒湿試験前／後のＨｃｊの差は約０．３ＭＡ／ｍであり、耐食性が悪いのがわかった。
【００１５】
（実施例２）
ＭｇＣｌ２添加量と耐食性との相関を調べるために以下の検討を行った。
実施例と同じ平均粒径２．５μｍのＳｍ２Ｆｅ１７Ｎ３微粉２０ｇが分散したスラリー（１試料分）を合計５試料分、及び表面処理用添加剤として実施例１と同じ溶液▲１▼、▲２▼を準備した。
［表面処理］
ＩＰＡ６０ｃｃ中にＳｍ２Ｆｅ１７Ｎ３微粉２０ｇが分散したスラリー（１試料分）をそれぞれ合計５個のビーカーに用意した。次に各ビーカーを７０℃に加熱し、次いで各ビーカー内のスラリーをスターラーで撹拌しながら▲１▼の溶液を４０ｃｃだけ２０分間かけて添加し、混合した。次に各スラリー中のＳｍ２Ｆｅ１７Ｎ３微粉表面にリン酸化合物皮膜が極力均一に被覆されるように各ビーカーの上澄み液を５０ｃｃ捨てた。次に▲２▼の溶液をそれぞれ２．５，５．０，７．５，１０．０，１２．５，２５．０，５０．０及び６２．５ ｃｃを各スラリーに添加後１０分間スターラーで撹拌し、次いで上澄み液を捨てた。これら一連の処理の間、各スラリーは７０℃に保持された。次に窒素気流中で室温で乾燥した。次にロータリーポンプで真空排気しつつ２２０℃で１時間加熱し、次いで室温まで冷却して本発明によるリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を得た。
次に、前記リン酸化合物被覆を８０℃、相対湿度（ＲＨ）９０％に保持した恒温恒湿槽に入れて１６時間保持し、次いで室温の大気中に戻す恒温恒湿試験を行った。
図３に示すように恒温恒湿試験前／後のリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉の室温の固有保磁力Ｈｃｊ（ＶＳＭにより測定）の変化幅は０．２ＭＡ／ｍ未満であり、スラリー中のＩＰＡ５０ｃｃへのＮａＯＨ添加量が０．００５ｇ以上であるとき、つまり有機溶媒１００ｃｃへのＮａＯＨ添加量が０．０１ｇ以上であるときに特に良好な耐食性が付与される。
（比較例３）
ＩＰＡ６０ｃｃ 中にＳｍ２Ｆｅ１７Ｎ３微粉２０ｇが分散したスラリー（１試料分）をビーカーに移して７０℃に加熱した。次にビーカー内のスラリーをスターラーで撹拌しながら▲１▼の溶液を４０ｃｃだけ２０分間かけて添加し、混合した。次にＭｇＣｌ２を添加せずに窒素気流中で室温で乾燥した。次にロータリーポンプで真空排気しつつ２２０℃で１時間加熱し、次いで室温まで冷却して比較例のリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を得た。以降は実施例２と同様の恒温恒湿試験を行い、恒温恒湿試験前／後のリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉のＨｃｊを測定した。測定結果を図３に示すが、ＭｇＣｌ２未添加のリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉はＭｇＣｌ２を所定量添加して得られたリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉に比べて耐食性に劣るのがわかる。
【００１６】
（実施例３）
リン酸添加量と耐食性との相関を調べるために以下の検討を行った。
［表面処理用添加剤］
スラリーに添加する表面処理剤として、実施例１と同じリン酸を用いて１００ｃｃのＩＰＡに溶解するリン酸添加量を変化させた以下の溶液▲３▼、▲４▼、▲５▼を準備した。また実施例１と同じ溶液▲２▼を使用した。
▲３▼リン酸０．７５ｇを１００ｃｃのＩＰＡに溶解した溶液、▲４▼リン酸０．５０ｇを１００ｃｃのＩＰＡに溶解した溶液、▲５▼リン酸０．２５ｇを１００ｃｃのＩＰＡに溶解した溶液
［表面処理］
ＩＰＡ６０ｃｃ中にＳｍ２Ｆｅ１７Ｎ３微粉２０ｇが分散したスラリー（１試料分）をそれぞれ合計３個のビーカーに用意した。次に各ビーカーを７０℃に加熱し、次いで各スラリーをそれぞれスターラーで撹拌しながら▲３▼、▲４▼及び▲５▼の溶液をそれぞれ４０ｃｃだけ２０分間かけて添加し、混合した。次に各ビーカーの上澄み液を４０ｃｃ捨てた。次に▲２▼の溶液１０ｃｃ及びＩＰＡ３０ｃｃを添加後１０分間スターラーで撹拌し、次いで上澄み液を捨てた。これら一連の処理の間、各スラリーは７０℃に保持された。次に窒素気流中で室温で乾燥した。次にロータリーポンプで真空排気しつつ２２０℃で１時間加熱し、次いで室温まで冷却して本発明によるリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を得た。
次に、前記リン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を８０℃、相対湿度（ＲＨ）９０％に保持した恒温恒湿槽に入れて１６時間保持し、次いで室温の大気中に戻す恒温恒湿試験を行った。
図４に示すように恒温恒湿試験後のリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉の室温のＨｃｊ（ＶＳＭにより測定）は０．２ＭＡ／ｍを超えているのがわかる。また図４から、有機溶媒１００ｃｃへのリン酸添加量が０．２ｇ以上であるとき特に良好な耐食性が付与されるのがわかる。
（比較例４）
ＩＰＡ６０ｃｃ中にＳｍ２Ｆｅ１７Ｎ３微粉２０ｇが分散したスラリー（１試料分）をビーカーに入れて７０℃に加熱した。次にスラリーをスターラーで撹拌しながら▲２▼の溶液１０ｃｃ及びＩＰＡ３０ｃｃを添加後１０分間スターラーで撹拌し、次いで上澄み液を捨てた。これら一連の処理の間、スラリーは７０℃に保持された。次に窒素気流中で室温で乾燥した。次にロータリーポンプで真空排気しつつ２２０℃で１時間加熱し、次いで室温まで冷却して比較用のリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を得た。
以降は実施例３と同様の恒温恒湿試験を行い、恒温恒湿試験前／後のＨｃｊを測定した。測定結果を図４に示す。
リン酸未添加のリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉はリン酸を所定量添加して得られたリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉に比べて耐食性に劣るのがわかる。
【００１７】
（実施例４）
処理温度を７０℃とし、添加する金属化合物を表１のごとく替えた他は実施例１と同様にリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を得て、恒温恒湿試験前／後の室温の固有保磁力Ｈｃｊ（ＶＳＭにより測定）を測定した。結果を表１に併記する。
【００１８】
【表１】
【００１９】
（実施例５）
実施例１で作製したリン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉を用いて、ボンド磁石を作製した。
リン酸化合物被覆Ｓｍ２Ｆｅ１７Ｎ３微粉９ｋｇ（９０重量％）と、バインダ樹脂としてナイロン１２（製品名Ｌ１６４０：ダイセル・デグサ社製）の粉末０．９５ｋｇ（９．５重量％）と、滑剤としてステアリン酸の粉末０．０５ｋｇ（０．５重量％）をＶ型混合器で混合し、混合物を作製した。この混合物を２軸連続押出成形機を用いて加熱温度２４０℃で混練、成形し、ストランドカッターでペレットを作製した。更に、ペレットを射出成形機を用いて、加熱温度２５０℃の磁場中で配向した状態で成形し、直径２８ｍｍ厚さ０．４ｍｍの円盤状のボンド磁石成形体を作製した。
このボンド磁石について相対湿度（ＲＨ）９０％に保持した恒温恒湿槽に入れて１６時間保持し、次いで室温の大気中に戻す恒温恒湿試験を行い、室温のＨｃｊをＶＳＭにより測定した。結果を表２に示す。
【００２０】
（比較例５）
表面処理を施していないＳｍ２Ｆｅ１７Ｎ３微粉を用いて、実施例５と同様にボンド磁石を作製、恒温恒湿試験を行い、室温のＨｃｊをＶＳＭにより測定した。結果を表２に示す。
【００２１】
【表２】
【００２２】
【発明の効果】
本発明によれば、耐食性の良好な希土類ボンド磁石を製造可能な、リン酸と金属化合物を用いた新規な希土類磁石粉末の表面処理方法を提供することができる。
【図面の簡単な説明】
【図１】リン酸化合物処理温度と実施例のＳｍ−Ｆｅ−Ｎ系磁粉のＨｃｊとの関係を示す図である。
【図２】リン酸化合物処理温度と比較例のＳｍ−Ｆｅ−Ｎ系磁粉のＨｃｊとの関係を示す図である。
【図３】本発明に係わるＭｇＣｌ２添加量とＳｍ−Ｆｅ−Ｎ系磁粉のＨｃｊとの関係の一例を示す図である。
【図４】本発明に係わるリン酸添加量とＳｍ−Ｆｅ−Ｎ系磁粉のＨｃｊとの関係の一例を示す図である。[0001]
[Technical field to which the present invention belongs]
The present invention relates to a novel rare earth magnet powder surface treatment method using phosphoric acid and a metal compound.
[0002]
[Prior art]
Rare-earth bonded magnets have poorer corrosion resistance than rare-earth sintered magnets, and rust generation and magnetic properties are remarkably reduced particularly in a high-temperature and high-humidity atmosphere. Therefore, further improvement of the surface treatment method is required.
Japanese Patent Application Laid-Open No. 2002-124406 discloses that a predetermined amount of phosphoric acid is added at the time of pulverizing a rare-earth magnet powder, and then the powder is dried in an inert gas or in a vacuum at a temperature of 100 ° C. or more and less than 400 ° C. to obtain weather resistance. There is a disclosure that the production of bonded magnets having significantly improved and thus high weather resistance is possible.
However, according to the study of the present inventors, the surface treatment method described in the example of this publication substantially corresponds to Comparative Example 3 described below, and the corrosion resistance is not sufficient, leaving room for improvement. all right.
[0003]
In addition, in the formation mechanism of 3.1.3 iron phosphate-based film on page 34 of “Chemical conversion treatment of metal” (published by Riko Publishing Co., Ltd., written by Fujio Mamiya), “as a treatment liquid used in the iron phosphate-based coating method” An aqueous solution containing sodium dihydrogen phosphate and a surfactant, and simultaneously performing film formation and degreasing ”. However, it was found that even when the rare earth magnet powder was coated with a phosphate compound using this treatment liquid, the corrosion resistance was not significantly improved as shown in Comparative Example 5 described later.
[0004]
[Patent Document 1]
JP-A-2002-124406 (page 5, left column, line 20 to right column, line 14, table 1)
[Non-patent document 1]
Fujio Mamiya, Chemical Conversion of Metals, published by Riko Publishing Co., Ltd., September 15, 1973, pp. 34-35
[0005]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide a novel rare earth magnet powder surface treatment method using phosphoric acid and a metal compound, which can produce a rare earth bonded magnet having good corrosion resistance.
[0006]
[Means for Solving the Problems]
The surface treatment method of the rare earth magnet powder of the present invention that has solved the above-mentioned problem is to prepare a slurry in which the rare earth magnet powder is dispersed in an organic solvent, then add phosphoric acid to the slurry, and then add a metal compound to the slurry. And then heating to 50 to 300 ° C. in a vacuum or an inert gas atmosphere.
It is preferable that the metal compound is added in a state of being dissolved in an organic solvent, since the corrosion resistance of the rare earth magnet powder is remarkably improved.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
The rare earth magnet powder to which the surface treatment method of the present invention is applied is not particularly limited, and any rare earth magnet powder for a rare earth bonded magnet is applicable.
As a specific example, an RTB-based magnet powder (R is at least one kind of rare earth element containing Y and T is Fe or Fe and Co. For example, Nd-Fe-B-based magnet powder or the like), or R '-T'-N based magnet powder (R 'is at least one kind of rare earth element including Y and T' is Fe or Fe and Co. For example, Sm-Fe-N based magnet powder and the like).
[0008]
The organic solvent constituting the slurry must have an effect of shielding at least the rare earth magnet powder in the slurry from the atmosphere and suppressing oxidation. Examples include alcohols such as ethanol, methanol or propyl alcohol, ketones, lower hydrocarbons or aromatic compounds. Further, for example, mineral oil, synthetic oil or vegetable oil can be used.
[0009]
In order to obtain good corrosion resistance, the amount of the rare earth magnet powder and phosphoric acid in the slurry should be 0.15 to 1.0 g / 100 cc and 0.2 to 0.5 g / 100 cc with respect to the organic solvent. Is preferred. If the amount of phosphoric acid is less than 0.15 g / 100 cc, the corrosion resistance is not improved, and if it exceeds 1.0 g / 100 cc, excess phosphoric acid is wasted. The amount of phosphoric acid to be added here is based on an amount corresponding to an aqueous solution having a concentration of 85% by mass. For example, when using another concentration, the concentration may be converted into a concentration of 85% by mass.
[0010]
The metal compound used in the present invention is not particularly limited. For example, a metal compound soluble in an organic solvent (alcohol or the like) is preferable. Among the metal compounds, hydroxides, carbonates, halides, nitrates, nitrites, alcoholates, chelate compounds, alkylated compounds and the like are useful. Further, as the metal element contained in the metal compound, a metal element which reacts with phosphoric acid to generate a phosphate and the phosphate is poorly water-soluble is preferable. For example, Na, K, etc., which are alkali metals, Mg, Ca, Nd, Sm, etc., which are rare earth metals, B, Al, Si, etc., which are other typical metals, and Ti, Zr, Cr, Mo, Mn which are transition metals. , Fe, Co, Ni, Cu, Ag, Zn and the like, but are not particularly limited thereto.
In order to obtain good corrosion resistance, the addition amount of the metal compound to the organic solvent in the slurry is preferably 0.005 to 0.2 g / 100 cc, and more preferably 0.01 to 0.1 g / 100 cc. If the amount of the metal compound is less than 0.005 parts by weight, it is difficult to improve the corrosion resistance, and if it exceeds 0.2 parts by weight, the effect of improving the corrosion resistance is saturated.
[0011]
The slurry after adding the solution of the metal compound and mixing is heated to 50 to 300 ° C. in a vacuum or an inert gas atmosphere and dried. Then cool to room temperature. If the heating temperature is lower than 50 ° C., the corrosion resistance is deteriorated, and if the heating temperature is higher than 300 ° C., the thermal demagnetization of the rare earth magnet powder cannot be ignored.
[0012]
The average thickness of the phosphate compound film formed on the surface of the rare earth magnet powder by the surface treatment method of the present invention is about 5 to 50 nm.
[0013]
Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.
[0014]
(Example 1)
The following study was conducted to examine the correlation between the heating conditions after the phosphate compound coating treatment and the corrosion resistance.
[Preparation of Slurry Used for Surface Treatment] 2-17 type Sm 2 Fe 17 N 3 coarse powder of 100 mesh under was finely pulverized by a wet ball mill using isopropyl alcohol (hereinafter abbreviated as IPA) as a solvent to obtain an average particle size of 2 A slurry (for one sample) in which 20 g of 0.5 μm (measured by an air permeation method) Sm 2 Fe 17 N 3 fine powder was dispersed was prepared for a total of four samples.
[Surface treatment additives]
The following (1) and (2) were prepared as surface treatment agents to be added to the slurry.
(1) A solution in which 0.75 g of phosphoric acid is dissolved in 100 cc of IPA (phosphoric acid is an aqueous solution having a concentration of 85% by mass, manufactured by Kanto Chemical Co., Ltd.)
{Circle over (2)} Solution of 0.2 g of MgCl 2 dissolved in 100 cc of IPA [Surface treatment]
A slurry (for one sample) in which 20 g of Sm 2 Fe 17 N 3 fine powder was dispersed in 60 cc of IPA was prepared in a total of four beakers. Next, each beaker was heated to 20, 40, 60 and 80 ° C., respectively, and while stirring the slurry in each beaker with a stirrer, 40 ml of the solution (1) was added over 20 minutes and mixed. The amount of phosphoric acid added in this case is equivalent to 0.3 g / beaker). The reason for adding the solution (1) is to form a phosphate compound film as uniform as possible. Next, 50 cc of the supernatant of each beaker was discarded so that a phosphate compound film was formed as uniformly as possible on the surface of the Sm 2 Fe 17 N 3 fine powder in each slurry. Next, after adding 50 cc of the solution (2), the mixture was stirred with a stirrer for 10 minutes, and then the supernatant was discarded. During these series of treatments, the slurry in each beaker was maintained at 20, 40, 60 and 80 ° C, respectively. Next, it was dried at room temperature in a stream of nitrogen. Next, the mixture was heated at 220 ° C. for 1 hour while evacuating with a rotary pump, and then cooled to room temperature to obtain a phosphate compound-coated Sm 2 Fe 17 N 3 fine powder according to the present invention.
Next, the phosphoric acid compound-coated Sm 2 Fe 17 N 3 fine powder was placed in a thermo-hygrostat maintained at 80 ° C. and a relative humidity (RH) of 90%, maintained for 13 hours, and then returned to the room temperature atmosphere. A moisture test was performed.
As shown in FIG. 1, the change width of the room-temperature intrinsic coercive force Hcj (measured by VSM) of the phosphate compound-coated Sm 2 Fe 17 N 3 fine powder before / after the constant temperature / humidity test was small, and the surface treatment method of the present invention It can be seen that good corrosion resistance was imparted. FIG. 1 also shows that the treatment temperature of the phosphoric acid compound is preferably 40 to 80 ° C., and more preferably 60 to 80 ° C., where the difference in Hcj before and after the constant temperature and constant humidity test is small.
(Comparative Example 1)
A phosphoric acid compound-coated Sm 2 Fe 17 N 3 fine powder dried at room temperature in a nitrogen stream in the same manner as in Example 1 was obtained. The same temperature and humidity test as in Example 1 was performed on the fine powder that had not been subjected to the vacuum heat treatment. As shown in FIG. 2, the change width of the intrinsic coercive force Hcj (measured by VSM) at room temperature of the phosphate compound-coated Sm 2 Fe 17 N 3 fine powder before / after the constant temperature / humidity test was larger than that in FIG. It was found that the corrosion resistance was worse than that of No. 1.
(Comparative Example 2)
The following examination was conducted to confirm the effect of adding the solution ( 2 ) (IPA dilution effect of MgCl 2 ).
In the same manner as in Example 1, processing was performed until 50 cc of the supernatant of the beaker was discarded so that the phosphate compound film was coated as uniformly as possible on the surface of the Sm 2 Fe 17 N 3 fine powder in the slurry. Next, instead of the solution ( 2), 0.2 g of MgCl 2 was directly added to the slurry, and the mixture was stirred with a stirrer for 10 minutes. During these series of processes, the slurry in the beaker was kept at 60 ° C. Thereafter, a phosphoric acid compound-coated Sm 2 Fe 17 N 3 fine powder of a comparative example was obtained in the same manner as in Example 1. The difference in Hcj before and after the constant temperature / humidity test of this derivative was about 0.3 MA / m, indicating that the corrosion resistance was poor.
[0015]
(Example 2)
The following study was conducted to investigate the correlation between the amount of added MgCl 2 and the corrosion resistance.
A slurry (1 sample) in which 20 g of Sm 2 Fe 17 N 3 fine powder having an average particle diameter of 2.5 μm was dispersed as in the example was used for a total of 5 samples, and the same solution as in Example 1 as a surface treatment additive (1) And (2) were prepared.
[surface treatment]
A slurry (for one sample) in which 20 g of Sm 2 Fe 17 N 3 fine powder was dispersed in 60 cc of IPA was prepared in a total of five beakers. Next, each beaker was heated to 70 ° C. Then, while stirring the slurry in each beaker with a stirrer, 40 cc of the solution (1) was added over 20 minutes and mixed. Next, 50 cc of the supernatant of each beaker was discarded so that the phosphate compound film was coated as uniformly as possible on the surface of the Sm 2 Fe 17 N 3 fine powder in each slurry. Next, 2.5, 5.0, 7.5, 10.0, 12.5, 25.0, 50.0 and 62.5 cc of the solution of (2) was added to each slurry, and the mixture was stirred for 10 minutes. And the supernatant was discarded. Each slurry was kept at 70 ° C. during these series of treatments. Next, it was dried at room temperature in a stream of nitrogen. Next, the mixture was heated at 220 ° C. for 1 hour while evacuating with a rotary pump, and then cooled to room temperature to obtain a phosphate compound-coated Sm 2 Fe 17 N 3 fine powder according to the present invention.
Next, a constant temperature and humidity test was performed in which the phosphoric acid compound coating was placed in a constant temperature and humidity chamber maintained at 80 ° C. and a relative humidity (RH) of 90% for 16 hours, and then returned to the room temperature atmosphere.
As shown in FIG. 3, the change width of the room temperature intrinsic coercive force Hcj (measured by VSM) of the phosphate compound-coated Sm 2 Fe 17 N 3 fine powder before / after the constant temperature / humidity test is less than 0.2 MA / m, Particularly good corrosion resistance is provided when the amount of NaOH added to 50 cc of IPA in the slurry is 0.005 g or more, that is, when the amount of NaOH added to 100 cc of the organic solvent is 0.01 g or more.
(Comparative Example 3)
A slurry (for one sample) in which 20 g of Sm 2 Fe 17 N 3 fine powder was dispersed in 60 cc of IPA was transferred to a beaker and heated to 70 ° C. Next, while stirring the slurry in the beaker with a stirrer, the solution of (1) was added by 40 cc over 20 minutes and mixed. Next, drying was performed at room temperature in a nitrogen stream without adding MgCl 2 . Next, the mixture was heated at 220 ° C. for 1 hour while evacuating with a rotary pump, and then cooled to room temperature to obtain a phosphoric acid compound-coated Sm 2 Fe 17 N 3 fine powder of a comparative example. Thereafter, the same constant temperature and humidity test as in Example 2 was performed, and the Hcj of the phosphate compound-coated Sm 2 Fe 17 N 3 fine powder before and after the constant temperature and constant humidity test was measured. The measurement results are shown in FIG. 3, phosphate compound coated Sm 2 Fe 17 N 3 fine powder of MgCl 2 not added compared with MgCl 2 in phosphate compound coated Sm 2 Fe 17 N 3 fine powder obtained by adding a predetermined amount It is understood that the corrosion resistance is poor.
[0016]
(Example 3)
The following study was conducted to investigate the correlation between the amount of phosphoric acid added and the corrosion resistance.
[Surface treatment additives]
As surface treatment agents to be added to the slurry, the following solutions (3), (4) and (5) were prepared using the same phosphoric acid as in Example 1 and changing the amount of phosphoric acid dissolved in 100 cc of IPA. . The same solution (2) as in Example 1 was used.
(3) a solution of 0.75 g of phosphoric acid in 100 cc of IPA, (4) a solution of 0.50 g of phosphoric acid in 100 cc of IPA, and (5) a solution of 0.25 g of phosphoric acid in 100 cc of IPA. [surface treatment]
A slurry (for one sample) in which 20 g of Sm 2 Fe 17 N 3 fine powder was dispersed in 60 cc of IPA was prepared in a total of three beakers. Next, each beaker was heated to 70 ° C., and then each of the solutions (3), (4), and (5) was added in an amount of 40 cc over 20 minutes while stirring each slurry with a stirrer, and mixed. Next, 40 cc of the supernatant of each beaker was discarded. Next, 10 cc of the solution (2) and 30 cc of IPA were added and the mixture was stirred with a stirrer for 10 minutes, and the supernatant was discarded. Each slurry was kept at 70 ° C. during these series of treatments. Next, it was dried at room temperature in a stream of nitrogen. Next, the mixture was heated at 220 ° C. for 1 hour while evacuating with a rotary pump, and then cooled to room temperature to obtain a phosphate compound-coated Sm 2 Fe 17 N 3 fine powder according to the present invention.
Next, the phosphoric acid compound-coated Sm 2 Fe 17 N 3 fine powder was placed in a thermo-hygrostat maintained at 80 ° C. and a relative humidity (RH) of 90%, maintained for 16 hours, and then returned to room temperature air. A moisture test was performed.
As shown in FIG. 4, it can be seen that the room temperature Hcj (measured by VSM) of the phosphate compound-coated Sm 2 Fe 17 N 3 fine powder after the constant temperature and humidity test exceeds 0.2 MA / m. FIG. 4 shows that particularly good corrosion resistance is imparted when the amount of phosphoric acid added to 100 cc of the organic solvent is 0.2 g or more.
(Comparative Example 4)
A slurry (for one sample) in which 20 g of Sm 2 Fe 17 N 3 fine powder was dispersed in 60 cc of IPA was placed in a beaker and heated to 70 ° C. Next, while stirring the slurry with a stirrer, 10 cc of the solution (2) and 30 cc of IPA were added, the mixture was stirred with a stirrer for 10 minutes, and the supernatant was discarded. The slurry was kept at 70 ° C. during these series of treatments. Next, it was dried at room temperature in a stream of nitrogen. Next, the mixture was heated at 220 ° C. for 1 hour while evacuating with a rotary pump, and then cooled to room temperature to obtain a comparative phosphoric acid compound-coated Sm 2 Fe 17 N 3 fine powder.
Thereafter, a constant temperature and humidity test similar to that in Example 3 was performed, and Hcj before and after the constant temperature and humidity test was measured. FIG. 4 shows the measurement results.
Phosphate compound coated Sm 2 Fe 17 N 3 fine powder of phosphoric acid was not added is seen that the poor corrosion resistance as compared with the phosphate compound-coated Sm 2 Fe 17 N 3 fine powder obtained by adding a predetermined amount of phosphoric acid.
[0017]
(Example 4)
A phosphoric acid compound-coated Sm 2 Fe 17 N 3 fine powder was obtained in the same manner as in Example 1 except that the treatment temperature was set to 70 ° C. and the added metal compound was changed as shown in Table 1, and the room temperature before and after the constant temperature and humidity test was performed. Was measured for intrinsic coercive force Hcj (measured by VSM). The results are also shown in Table 1.
[0018]
[Table 1]
[0019]
(Example 5)
Using the phosphoric acid compound-coated Sm 2 Fe 17 N 3 fine powder produced in Example 1, a bonded magnet was produced.
9 kg (90 wt%) of phosphoric acid compound-coated Sm 2 Fe 17 N 3 fine powder, 0.95 kg (9.5 wt%) of nylon 12 (product name L1640: manufactured by Daicel Degussa) as a binder resin, and a lubricant As a mixture, 0.05 kg (0.5% by weight) of stearic acid powder was mixed with a V-type mixer to prepare a mixture. This mixture was kneaded and molded at a heating temperature of 240 ° C. using a twin-screw continuous extruder, and pelletized with a strand cutter. Further, the pellets were molded using an injection molding machine in a state where they were oriented in a magnetic field at a heating temperature of 250 ° C., to produce a disc-shaped bonded magnet molded body having a diameter of 28 mm and a thickness of 0.4 mm.
The bonded magnet was placed in a thermo-hygrostat kept at 90% relative humidity (RH), held for 16 hours, then returned to room temperature in the air and subjected to a thermo-hygro test, and Hcj at room temperature was measured by VSM. Table 2 shows the results.
[0020]
(Comparative Example 5)
Bond magnets were prepared in the same manner as in Example 5 using Sm 2 Fe 17 N 3 fine powder that had not been subjected to surface treatment, subjected to a constant temperature and humidity test, and Hcj at room temperature was measured by VSM. Table 2 shows the results.
[0021]
[Table 2]
[0022]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the surface treatment method of the rare earth magnet powder using phosphoric acid and a metal compound which can manufacture the rare earth bonded magnet with favorable corrosion resistance can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a phosphate compound treatment temperature and Hcj of an Sm—Fe—N-based magnetic powder of an example.
FIG. 2 is a diagram showing a relationship between a phosphoric acid compound treatment temperature and Hcj of an Sm—Fe—N-based magnetic powder of a comparative example.
FIG. 3 is a graph showing an example of the relationship between the amount of MgCl 2 added and Hcj of Sm—Fe—N-based magnetic powder according to the present invention.
FIG. 4 is a graph showing an example of the relationship between the amount of phosphoric acid added and Hcj of Sm—Fe—N-based magnetic powder according to the present invention.
